Patent GB-1016631-A (GB)
Title: Television signal processing apparatus
Inventor: BALDWIN JOHN LEWIS EDWIN
IPC: H04N5/04
Filed: 1962-03-04
Abstract: 1,016,631. Television. RANK-BUSH MURPHY Ltd. March 4, 1963 [March 4, 1962], No. 43255/61. Heading H4F.  A television signal A, Fig. 1, received from a source (e.g. a long range radio link or a magnetic recording) of a character such that minor but deleterious errors occur in the timing t 1 , t 2  of the synchronizing components is blanked throughout the blanking intervals so as to eliminate the synchronizing components as shown at B and is then reformed as shown at F with regenerated synchronizing components E, the timing of the leading edges of components E being controlled by a train of impulses repetitive at twice mean horizontal frequency and of which the phase is rigidly locked to the mean phase of the original horizontal synchronizing components, and the timing of the trailing edges of components E being controlled by the rear edges of the original synchronizing components. The invention provides a method of re-establishing correctly timed synchronizing signals without regenerating a completely new train of composite synchronizing' signals. In Figs. 2 and 3 the original television signal G is separated at 2 into the blanked picture component H and the synchronizing component J which is applied to control the phase of an oscillator 5 which produces impulses K at twice horizontal frequency and is connected in a conventional flywheel synchronizing system including a phase comparitor 4. The impulse frequency is divided by two by a divider circuit 6 which is controlled by a-phase comparitor 7 receiving the synchronizing component J so as to prevent phase ambiguity. The frame synchronizing component L is separated in a circuit 9. The output from divider 6 is then added to component L in OR gate 8 and the combined signal added to impulse train K in AND gate 10. The resulting signal M comprises a succession of horizontal frequency pulses which is interrupted by a train of pulses of twice this frequency during each frame synchronizing signal. Signal M is applied to control the leading edges of pulses produced by a pulse generator 12, whilst the trailing edges are timed by the trailing edges of the original synchronizing component J. The generated pulse waveform N thus comprises a regenerated composite synchronizing component with any timing errors eliminated from the leading edges. Waveform N is combined with the blanked signal H in a mixer stage 13 to produce finally a composite television signal P. The timing of the leading edges of the regenerated pulses may be altered by inserting a delay circuit in lead 11 or in the feedback connection from oscillator 5 to phase comparitor 4. The timing of the trailing edges may be controlled by inserting a delay circuit in the connection from separator circuit 2 to pulse generator 12. The timing of the synchronizing pulses as a whole with reference to the picture components may be controlled by inserting a delay circuit in lead 3. A second embodiment of the invention, Figs. 4-6 (not shown), involves the same general principles but is described in greater detail. The original television signal, which is subject to D.C. clamping and " black and " white limiting, is blanked (at a level slightly less the " black ") under the control of a composite blanking signal which is timed by the phase-locked impulse train at twice mean horizontal frequency. The pulse train which is employed to time the onset of the regenerated synchronizing pulses is controlled so as to include pulses at twice horizontal frequency for only a part of the frame blanking interval. In connection with this embodiment, Specification 984,443 is referred to for a sawtooth generator which forms part of the flywheel synchronizing circuit for generating the phaselocked impulse train, Specification 995,445 is referred to for a pulse-generating circuit and Specification 1,002,782 is referred to for a D.C. restoration circuit.